We are requesting funds to purchase a Zeiss LSM 510 META NLO on an upright epifluorescence Axioplan 2 microscope. Over the last several years, the invention of multiphoton (two-photon laser scanning) microscopy has spearheaded cellular research into new realms, providing real-time views of cell morphology, function and development within the living animal Multiphoton microscopy uses high-energy infrared pulses to excite fluorophores, therefore enabling imaging of structures deep (hundreds of micrometers) within the tissue. Another advantage of multiphoton imaging is that living specimens can be imaged repeatedly over long periods of time (hours to weeks). This is because excitation is effectively confined to the focal point of the beam, such that fluorophores above and below are not excited. Photobleaching and phototoxicity, common limitations of confocal microscopy, are thus much reduced when using multiphoton microscopy. This microscope will be used to support the ongoing, funded research programs of three primary investigators in two different departments at the University of Washington. Although these studies will focus on basic mechanisms of neural development and plasticity, the findings will have implications for research in neuroscience and neurological diseases, ophthalmology and vision research and deafness and auditory dysfunction. The requested instrument would be housed in the Biological Structure Imaging facility, and would be administered and maintained by funds from the department. The proposed administrative structure and management of the instrument are optimized for the best utilization of the microscope time, thus assuring the maximum benefit to the primary investigators, as well as a broad range of secondary users at the University. [unreadable] [unreadable] [unreadable]